348 Predicting baking performance using biaxial extensional rheology.

B. J. DOBRASZCZYK and J. D. Schofield. Department of Food Science & Technology, University of Reading, U.K.

Baking is about the growth and stability of bubbles. The size, distribution, growth and failure of these bubbles during baking has a major impact on the final quality of the bread in terms of both appearance (texture) and final volume. The limit of expansion is related directly to their stability, due to coalescence and the eventual loss in gas retention on bubble rupture. The rheological properties of the bubble walls will be important in maintaining stability against premature failure during baking. Conventional dynamic rheological tests carried out in shear under small deformations and high strain rates are inappropriate to baking, because they are carried out at rates and conditions very different from those experienced by the dough during baking expansion. In terms of deformation, the relevant conditions during breadmaking are biaxial extension, large strains and low strain rates. Previous work has shown that the stability of failure in single dough bubble walls is related directly to the extensional strain hardening properties of the dough, and that strain hardening plays an important role in the stabilisation of bubble walls during baking. We are evaluating a new rheological method to predict breadmaking performance using a modified bubble inflation technique, which measures the extensional rheological properties of doughs and glutens in biaxial extension under conditions of deformation relevant to breadmaking.